1. Field of the Invention
This invention relates generally to a vibration absorber, damper, or telescoping strut for a motor vehicle, which damper, or strut, can have a mechanical device, or tension limit stop, for limiting movement of a piston rod within a cylinder thereof. In general, such a vibration damper can have a cylinder in which a piston, having damping devices and being connected to a piston rod, can be moved axially. The piston can typically divide the interior of the cylinder into two fluid-filled work chambers, one of which chambers can have a generally ring-shaped cross-section as defined between the interior of the cylinder wall and the piston rod. At one end of the cylinder there can generally be a guide and a seal for the piston rod. The hydraulic-mechanical tension limit stop, which can be located in the ring-shaped work chamber between the cylinder and the piston rod, can have a limit stop connected to the piston rod, and a spring which can contact, on one hand, the piston rod guide, and on the other hand, the limit stop.
2. Background Information
German Laid Open Patent Application No. 28 53 914, which corresponds to U.S. Pat. No. 4,345,748, discloses a mechanical limit stop for a vibration absorber or a telescoping strut which, among other things, has a spring which is located in the annular chamber between the piston rod and the cylinder. With this arrangement, after the piston rod has travelled a specified telescoping distance out of the cylinder, the spring comes into contact with a stop surface on the piston rod. In the embodiments illustrated therein, the spring, at its upper end, is centered in the vicinity of the piston rod guide on the inside diameter of the cylinder tube and, at its bottom end, is centered by the bottom end of the piston rod. The direct contact between the spring and the above-mentioned vibration absorber components during assembly and/or during operation of the absorber causes abrasion on the surfaces of the piston rod or on the cylinder tube, with the consequence that small chips can be formed which can have an adverse effect on the function of the vibration absorbers.
The embodiments illustrated in FIGS. 3 and 4 of German Laid Open Patent Application No. 28 53 914, and U.S. Pat. No. 4,345,748, have, on their lower end, a damping ring, which is intended to achieve a centering in relation to the piston rod by means of guide cams. But there are problems in making the connection between the spring and the molded-on damping ring., such that it is extremely difficult to guarantee reliable operation of the hydraulic-mechanical tension limit stop for the entire life of the device. For reasons relating to manufacturing technology, it is also essentially very difficult to mold around the spring, which means that the dimensional stability of the guide cams becomes imprecise. Consequently, the spring can scrape against the piston rod. Furthermore, on account of the particular type of connection between the spring and the damping ring, several coils of the spring are often embedded in the ring, and these embedded coils are thus essentially unavailable for the suspension process. Large stresses generally also occur inside the sleeve of the damping ring, which stresses threaten the connection to the spring.
An additional problem is the requirement for a simple but reliable suspension. With known devices, it can very often be a complex, time-consuming and expensive operation to reliably locate the upper end of the spring directly underneath the piston rod guide.